


The Grey Door

by FireFaceOutlook



Category: Undertale (Video Game)
Genre: M/M, Sanster, Snowdin, The Ruins (Undertale), Waterfall (Undertale)
Language: English
Status: In-Progress
Published: 2017-10-14
Updated: 2017-11-10
Packaged: 2019-01-17 03:28:04
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 2
Words: 2,478
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12356481
Author URL: https://archiveofourown.org/users/FireFaceOutlook/pseuds/FireFaceOutlook
Summary: A small smirk rose on Sans' face as he raised a fist and rapped it on the unusually cold wood.“knock knock.”He turned to continue to his station."͠W̡ho's t͏h̷er̨e̢?͝"̴





	1. Shave and a Haircut

**Author's Note:**

> **A/N: I guess the most important (and obvious) fact about this story is that Sans can see the grey door in Waterfall that (may or may not) leads to Gaster. Not much else has changed in this universe. Gaster was still the Royal Scientist in the past, Sans was his lab assistant, but one major difference is present here: Sans _doesn't_ remember Gaster, and Gaster's memory isn't exactly too well put together, with him being trapped in the Void and his soul shattered across time and space. I hope you will read and enjoy this story anyway.**

The doors in Snowdin Forest were Sans' favorite place to practice knock knock jokes. The lady behind the door was kind enough to humor him and, lately, she even began replying to him. Thinking of even more impressive jokes to tell to her every day kept him distracted during his sentry shifts; it was a better way to keep himself occupied than staring into nothing and waiting for a human that would never come. In fact, he was on his way to his second shift at the moment; the one in the middle of Waterfall. He decided to walk instead of taking a shortcut, since that would extend his free time before he had to commit to working, and that's when he came across it. In the passageway leading to his sentry station, there was a grey door in the wall that he'd never seen before. He stopped before it, tilting his head slightly as he examined it. It looked like the front door to his and Papyrus' house, just...grey. He reached for the doorknob, but discovered it was locked when it refused to budge.

“huh...” he uttered with a slight frown.

A small smirk rose on Sans' face as he raised a fist and rapped it on the unusually cold wood.

“knock knock.”

He turned to continue to his station.

"͠W̡ho's t͏h̷er̨e̢?͝"̴

Freezing mid-step, Sans' head slowly turned towards the door. Just like with the doors to the Ruins, he hadn't been expecting a reply.

His mind had gone blank in surprise, so he was really digging for a spectacular good joke. “beets?”

"B͜e͡e̵ts̡ w͠h̴o͘?͡"͘

“beets me.”

In the resulting silence, Sans began to sweat. That definitely wasn't the best joke in his arsenal... Knocking from the other side of the door made him jump.

“wh-who's there?”

"͝C҉er̶eal҉.̧"

“cereal who?”

"C̴er̶e҉al̸ ̛ple͢asu͜r̛e to meet you͞.̡"͜

Sans chuckled and under his own baritone voice, he could hear a tentative laugh joining in.

“my name's sans; sans the skeleton,” he offered.

“I'm Ga̢҉̛͝s͢͜͏̡͡ţ͏̢e̛͡r̴͠҉.”

“uh...” Whatever the guy had said was lost on Sans. It had sounded like a combination of static and something indescribable, and it made his head hurt to hear it. Instead of asking for that to be repeated, Sans said, “i'm just gonna call ya g, if you don't mind.”

"̛Tha͏t̸'s ̨fin͝e."̡

“look pal, i gotta go to work now. i'll see ya later.”

"G͝ǫo͢d̷by͡e, ̴Sa̸n̴s.̢"͞

During his shift, he couldn't keep his mind on creating jokes. Instead, his thoughts kept returning to the strange door and the mysterious man behind it. When his shift ended and he was free to go home for a nap before going to the station leading from Waterfall to the Hotlands, he decided to walk home. He didn't know if he got turned around at some point during his walk, but he didn't pass the grey door on the way.

  


It was a few weeks before he came across the door again. He swore on his soul that he took the same path to the Waterfall sentry station every time he walked, and the door just reappeared. He didn't know how it disappeared in the first place, but he didn't hesitate to approach it.

“knock knock,” he called after tapping out a short rhythm on the wood. It was as cold as he remembered.

"Sa҉ns.͘.͜.?͝"

“that's not how these joke work, g,” Sans chided.

A soft chuckle reached his ears (not that he had any), then G humored him. "͞A͢l͠right̵. ͝ Wh̷o'̕s͜ t̸h̢eŗe͡?"̕

“doris.”

"Dori̶s̷ wh̕o̴?"͘

“doris locked, that's why i had to knock.”

The silence came, just like last time, but Sans was a little less tense about it. A soft knocking echoed in the corridor.

“who's there?”

"҉Wat͡er.̶"

“water who?”

"Wat̛er y̕ou ͡doi͢n͝g? ̸ ̸Yo͠u'͢l͏l͡ ͘be ̨lat̕e fo͘r҉ ̴w͡o͞r͠k."̢

Sans pulled his phone out of his shorts and checked the time, then cursed when he realized that G was right.

“shit. i gotta go. see ya later!”

When he came back through – the same way he walked _to_ work; he double-checked –, the door wasn't there.

  


A few weeks passed before he saw it again.

  


“knock knock.”


	2. A New Anomaly

**Summary for the Chapter:**

> _“please don't make me do something like that again.”_

**Notes for the Chapter:**

> **A/N: I finally got chapter two out! I hope you guys like it -- _I_ like how it turned out. Also, just so you know, words that are bolded in the middle of sentences are signed and not spoken. The same does not apply for fully bolded sentences. Let me know what you think?**

Behind the Grey Door in Waterfall was a hallway, and that hallway led to a somewhat spacious room of off-white color and refractive shadows. It was as cold as a brisk night in Snowdin – or maybe a better comparison would be the paradoxical cold the lava in Hotland undoubtedly was, the kind that burned you _to the bone_. That was just how the Void took form around him. Gaster had found it unbearable when he first found himself trapped there, but after so long, the feeling just went _right through him_. (Sans would've liked those puns.) It was lonely, but at the same time, it was not. While he was not physically with them, three of his old coworkers, who had died during the Core incident, existed through pieces of his soul. He could only distantly feel the presence of two, and sometimes he heard sounds of the Core's mechanics through the third. He didn't know how many shards his soul had shattered into, but when he slept – which he did a lot, since there was little else to occupy his time – he often dreamed of rain or felt like he was sitting in the coldest corner of the Underground.

  


“knock knock!”

Gaster stirred from his perpetual slumber at Sans' familiar voice. He'd lost hold of his form at some point because he was nothing more than a puddle of black goo. It took a good chunk of energy to start pulling himself back together again into a looming, shapeless form with holey blobs for hands and a disfigured face.

“g...?”

He turned towards the hall, his body reacting agonizingly slow to his commands.

“̴̴̨͜S̴̷̕s̸̸̴͘͞s̷͟s̨͟͠͠͠a̶̡͘͟a̶̴̛͢͝a̶̴̶̢a̡͢͏̢a̧͜҉̷n̛͝͞n͟҉̴̴͝n̴̡͞҉n͜͏̸s̢͢ş͝ş̴s̷̡͞ş̷͡.̶͡.̨͘͜͠.͏̸̨”̵̧͜ he called, his voice wrenching itself from his half-made throat in a painful manner.

“... uh... you're doing that thing again. i can't understand you, pal.”

Gaster groaned softly. There was something happening with the timelines – an anomaly was twisting them to their whim, making them start and jump and end. And whenever a new timeline began, he found himself in the same position – a pool on the ground. Fortunately, this timeline didn't restart from the beginning, or Sans wouldn't be calling his name. (His nickname; the same nickname he used when they actually _knew_ each other. It hurt to be called it, but he knew that his name couldn't be heard by anyone who existed when he disappeared.) He put more effort into his body, a hint of white peering through the endless black and his fingers separating. He could feel his eye sockets, mouth, and the cracks on his face turning from melting openings to actual usable features.

"Is̶ t҉hi̧s ҉b͢e̡t̷ter̛, S҉an͠s...?͏"̢

He could never tell because when he spoke, whether it be Wingdings or Times New Roman, he sounded the same to himself. Though he had long forgotten how to speak in any but his own font. It was a miracle that Sans still understood him at all, even when Gaster taught him the basics of Wingdings. (As far as he knew, it was nigh impossible for other monsters to replicate his font by mouth, which was why he made up hand signs for it. Sans, Grillby, and Asgore were the few who could translate his language without reading his hands, and even then it was only when he was calm.)

“yep.” He heard a dull thump on the wood. “i have some time to spare before i have to go. wanna talk?”

Gaster did notice that Sans had arrived earlier than normal, now that he wasn't struggling with keeping himself in one piece.

"̵Ok҉ay͏.͢"̢ He walked – no, 'walked' isn't the right term; it was more like a glide – down the hall to the door, leaning against it. He could feel Sans' soul energy even through the wood. Sans wouldn't be able to feel him, since he only had a sliver of his own soul. "͡W͝ha̵t ̡w͝o͢u̕l҉d̴ ̧you ̛l͘ik̨e͡ ͝to ta҉lk ab͜out̷?̕"

“i don't know.” He heard the shorter skeleton slide to the ground, getting comfortable. “...how old are you, g?”

Gaster blinked, then laughed. "W̶h̡at͞ ҉k͡ind̵ of qu̕ęs͢t̶io̢n̕ i͠s ţhat?"

“i have a friend named grillby. he's pretty old, compared to a lot of monsters stuck down here. he even lived above ground, took part in the war.”

_I҉ ̷k͏ņow҉,_ Gaster thought.

He took part in the war as well, and he worked with Grillby more than once. That monster had spark, quite literally, and was what the humans feared most when they went into battle. He was the being of their darkest nightmares. _Hellfire_ , they called him. But even his might couldn't stop the humans from locking monsterkind in the mountain. 

“he'd never had too good of eye sight, though,” Sans continued. “so he doesn't really remember what stars looked like. so, i was wondering...” He sounded a little hopeful. 

"I'm ҉afr͢a̢id ͟my̛ ̨memo҉r̷y ͘i̵sn'̵t wh̷a͠t͢ ̴i̶t̨ ̵us̢ed͡ to be,̕ S̕an̡s.͞"͢ At least, it wasn't all too good at the moment. Today was one of his better days, though; he remembered Sans from the days in the lab, he remembered being in the war... "B̧e͝s̛ide̴s̷, ͠w҉o͡rd of mo͡ut͜h ͜des͠cri͟p̢ti̶ǫn͝s ju͠s̷t͘ wo̷ul͡dn't ͝d̶o ̡th͟e sigh̷t͞ jųst̨i̛c̢e͜. ͞ Y͡oư'҉l͏l̵ ͜se͜e ̸t̢he̵ ̶s͢t̡a̴rs͜ yourse҉lf one҉ ͏d͝ay.͠"

“if we ever get out of this hellhole,” Sans muttered. There was a scraping sound as Sans pushed off the door. “alright, i have to go. talk to you later, g.”

"҉Goo͘dbye,͡ Şan͟s͡."

  


That night, he dreamed of his time as a Royal Scientist.

  


_"̡T͞he҉r̶e'͜s ͠been͢ ͏a wa̡r̵ning ͢f̢or ͞a h̡ưm͜an, ҉Sa̕ns̡."͡ he sighed, staring into space, pen posed over the paperwork he was supposed to be working on while his free hand lazily signed along with his words. He was speaking in his font so eavesdroppers, which his other co-workers tended to be sometimes, wouldn't know the topic of conversation. He wasn't supposed to be telling anyone – Asgore asked him to keep it to himself –, but Sans was his personal assistant and close friend. He needed to confide in someone._

_“oh yeah?” Sans drawled, looking up from the quantum physics book he was reading. (Gaster pretended not to notice the thinner book hidden within.)_

_"҉I͘ w̶i̸s̷h͢ ͏we co͞ul҉d ͢stuḑy ̸them ̶l͡i̷ve͡,"̛ Gaster continued. “But͟ I woul̢d̨ ͝set҉t̵l̷e͜ ͟f̸or̷ ha̸v͠i͘ng̵ an͠o̴t̷h͝e͟r ͢h̨um̷an̕ so͡ul̢ to͡ ̶s̶t̡udy.”_

_Not that the King's child's soul wasn't an amazing source of scientific scrutiny, but there was only so much that could be done with it and its Determination at the moment._

_“why?” Sans asked. “i mean, we're already waiting on results_ **from the determination** _, aren't we?”_

_Gaster drummed his fingers on his desk. While Sans was his confidant, there were some things that he kept from him. Such as the fact that he and their other three co-workers had injected small amounts of Determination into their own souls. He would never let Sans or Alphys do something so dangerous. Besides, nothing had happened so far – it wasn't anything they needed to concern themselves with._

_“Yes͜. ͜But͟ th̕at̛'̴s j̧u҉s̢t ͠t̛he t̢h̡i͟n̶g͟. ͜ S̴a͝n͞s͠, ͟w̢ha͞t i̕f̕ th̵e͡re̴ ̸a̡re ̶m̢o̡re҉ ̢tr̨a̧its ̕for h͝um͢a̧n҉ ̡soųls ̡t̢ha͜n ͠D̨et͝er̨m̶ina͠t̨i͠o̢n?͠” He was beginning to grow excited. “Or̷ ͜ma̛y̴be ̸t̢he͘r̶e'̶s ͠e͏v̵en҉ d҉i͠ffer̨i̵ng ͘amo̷u҉nts ̕of ͟De͝termi͏n̸a͟tion͢ ͝i̷n e͟ąçh͘ s͡ơul, ͘d͘e҉p̴e̢nd̛ing ͢o͝n ̛the͏ ty͠p͜e o͟f h҉um̕an they are! T̡her͞e̵ ̢a̡r҉e s͟o̕ m͏any p͘ossib͡i̶l͘iţi͢es̢!͢ ҉ A͝n̢d͝ I̵ ̢ju͢s̸ţ ͡wa͡nt ̶th͢e͏ ̷cha͜nce̶ to ̨ştudy̴ m̕ore҉ ̶than͞ a ̸si͢n̶g̴l͘e ͡hum̴a̢n̛ ̢soul.”_

_He slumped down in his seat, tapping his pen on his cheekbone._

_Sans was silent for a moment. “hey, don't worry too much about it, g,” he said as he returned to his book. “i'm sure the royal guard will_ book _it here when they capture the soul.”_

_Gaster's shoulders shook briefly even as he cast Sans a disapproving look. “No puns in the lab, Sans.”_

_“i'll poke that funny bone of yours one day, doc.”_

_The rest of the day went much the same, with Sans spinning of puns while Gaster finished his paperwork. Gaster wasn't able to convince Sans to let him go home on his own, so they traveled to Waterfall together and Gaster wished Sans a good night and safe passage home._

  


_The next day, Sans was late to work, but that wasn't unusual. He was usually late one or two days a week. He always showed up sooner or later with some fantastic tale to tell, or with his brother in tow. With no paperwork to occupy him, Gaster was doing more physical work. He was helping with the construction of the Core. It was halfway done – it was a big project, but Gaster was more than happy to take part in it. After all, it was going to be his greatest creation. He only stopped for a break when he was paged by Alphys almost frantically. Sans must've finally arrived._

_It was quite the walk to get from the Core to the lab, but when he arrived, everyone passed was whispering and sounding excited, but they quieted when he passed. He was more than a little concerned about being pranked, but he didn't stop until he came to the main section of the lab. Sans and Alphys were sitting on one of the couches they had placed there for visitors. Sans was dressed in his normal clothes, but had on his blue jacket instead of his lab coat. That wasn't what really caught Gaster's attention, though. Sans' clothes had dirt and tears on them, and he had some discoloration on his skull and fingers, as if he was hit by and hitting something._

_“Sans...?”_

_Sans looked up and Gaster tensed at how hazy his eye lights were. He looked like he hadn't slept at all. He stood from his seat and Gaster glanced at Alphys as the other skeleton approached him. She shrugged helplessly and when Gaster looked down, it was in time to watch Sans push a glass container against his chest, looking away. In the container floated a soul of dark blue._

_“please don't make me do something like that again.”_

  


Gaster woke up to a new timeline again. But something was different this time. There was a new anomaly. He could sense it through the Void. How did he know it was a newcomer? The previous anomaly didn't have soul energy. It was just brimming with Determination. And this new anomaly was, too, but their soul energy was unmistakable. It was strong enough to be felt across the Underground, stronger than even Sans' had felt through the door – it was a human.

**"͏̴̶̛͠ ̶̕͟͞͡H҉̧̛ ̵͝o̵͏̢ ̸̷w̢҉͟   ̧҉͠͡ ̶͘i̴͘͜͝ ̵̷̛͡͠n̨͏ ̸̕͏t͡͞ ̨e̸͟͝ ̸r҉̷̨ ̷̕͞͡e͡ ̶̢͟͡s̨̨̛͡ t̵͞ ̸͘͢͟͝į̡̕ ͞͞n̴͏͜ ̵̕ģ̡͢͞͞ ̵̢͘.҉͞ ̵͠"̴̸̧̛**

**Notes for the Chapter:**

> **A/N: Here comes Frisk! How will they effect the Underground? We'll find out! So what should their first run be like? Neutral or Pacifist?**

**Author's Note:**

> **A/N: I know it's short, but the next chapter will probably be longer. This is just an introduction to this AU. Tell me what you think! (Also, if you didn't know, the title for the first chapter is a type of knocking pattern; just look it up if you don't know what it sounds like.)**


End file.
